(1) Field of the Invention
The present invention is directed generally to a unique kind of antifouling coating for use on marine vessels, and more specifically to an antifouling coating to prevent the accumulation of marine organisms/biomass on the submerged surfaces of marine vessels and equipment/hardware even when such objects are not moving.
(2) Description of the Prior Art
Unless protective measures are taken, any item submerged in marine waters will quickly become covered with both micro- and macroscopic fouling organisms. Biofouling of this nature is a serious concern to both the United States Navy and commercial maritime interests. This unwanted growth increases hydrodynamic drag, resulting in slower speeds and increased fuel usage. Biofouling can also interfere with the operation and performance of critical Navy systems such as SONAR equipment, underwater optical sensors and systems, special hull treatments, and any other equipment which is fully or partially submerged into bodies of water.
Each year a considerable amount of time and money is expended to groom ship and submarine hulls to remove marine biofouling. The traditional approach for the prevention of biofouling on marine vessel hulls has been to coat those hulls with a paint or coating loaded with a heavy-metal-based biocide. However the use of heavy-metal-based biocides is problematic, because such biocides do not degrade rapidly in the marine environment. This leads to the accumulation of toxic biocides in the sediment beneath many harbors and ports, which in turn can cause adverse effects on the health of non-targeted marine organisms and ecologies.
Microscopic level fouling is related to macro level fouling. Many studies have shown that if a biofilm of microbes cannot establish itself on a surface, then macro-scale fouling will not occur. Thus, it is desirable to control microscopic fouling or film formation on the surface.
Ablative technologies have been used in conjunction with some biocidal antifouling coatings to avoid the problem of a layer of organic material and dead microbes forming on and coating the surface of a hull, but typically ablation is not significant unless a vessel moves at moderate to high speeds.
The problem of microbe accumulation is particularly acute on vessels or equipment which is stationary in a marine environment (tied up at piers or docks or anchored to a fixed spot). Clearly, some kind of coating is needed that will refresh the exposed surface with biocide even if a vessel or device is not moving.
‘Foul-release’ technology utilizes coatings (such as silicones or highly fluorinated compounds) that exhibit low surface energy and thus present adhesion and bonding challenges for marine organisms. Since marine organisms cannot form strong bonds to such surfaces, they can be removed by the hydrodynamic forces exerted on such organisms by a vessel moving at or above a certain critical speed. However, foul release type coatings may not perform well on many vessels that tend to spend considerable time in port, or on stationary hardware, such as anchored buoys, since frequent, moderate-speed movement is needed to enable these coatings to keep hulls or other water-exposed surfaces free of fouling.
Water-soluble antifouling coatings are attractive candidates for protecting largely stationary vessels from marine biofouling. The problem with these technologies is controlling the rate of dissolution so that the coating will last for years rather than for days or months and incorporating an effective but environmentally friendly biocide within such a coating.
In view of the above problems, interest has increased in the development of more environmentally friendly technologies for preventing biofouling on ships, submarines and other maritime equipment and vessels.